1. Field of the Invention
The present invention generally relates to an information recording and reproducing apparatus and, more particularly, to a reproducing circuit for a magnetic recording and reproducing apparatus which amplifies a reproduction signal generated by a reproducing head and supplies the amplified reproduction signal to a signal processing circuit.
In recent years, a high frequency is used for signals reproduced by a magnetic disc apparatus in order to increase density and transfer speed of data. Thus, it is desirous to improve a high-frequency characteristic of a reproducing circuit which amplifies a signal generated by a magnetic head.
On the other hand, in the magnetic disc apparatus, the reproduction signal output from the magnetic head is supplied to a head IC through a transmission line such as a CAPS, a lead wire or a flexible pattern circuit (FPC), and the signal is amplified by the head IC. Such a transmission line has a capacitance and, thereby, the high-frequency characteristic of the reproduction signal is deteriorated and a cutoff frequency is decreased. Additionally, the high frequency characteristic of the reproduction signal is also deteriorated due to a frequency characteristic of the head IC.
Accordingly, it is desirous to improve the high frequency characteristic of the transmission line and the head IC so as to achieve an accurate transfer of the reproduction signal from the reproducing head to the head IC.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional magnetic disc apparatus. The conventional magnetic disc apparatus 100 shown in FIG. 1 records information on a magnetic disc 101 provided therein. The magnetic disc 101 is rotated by a spindle motor 102 in a direction indicated by arrow A. A magnetic head 103 is positioned above the magnetic disc 101 so as to record information on the magnetic disc 101 and read the information from the magnetic disc 101. The magnetic head 103 is supported on an end of an arm 104. The magnetic head 103 performs a recording operation or a reproducing operation while the magnetic head 103 is floated above the magnetic disc 101 due to a rotation of the magnetic disc 101.
The arm 104 is rotatably supported by a rotational shaft 105. An end of the arm 104 opposite to the end on which the magnetic head 103 is mounted is formed as a part of a voice coil motor 106. Thereby, the arm 104 can be rotated in directions indicated by arrows B about the rotational shaft 105 so that the magnetic head 103 is moved substantially in a radial direction of the magnetic disc 101.
The magnetic head 103 is connected to a head integrated circuit (head IC) 108 via a connection line 107. The connection line 107 comprises a lead wire and a flexible printed circuit (FPC). The head IC 108 is formed on the flexible printed circuit which can flexibly follow rotation of the arm 104 in the directions indicated by the arrows B. The head IC 108 amplifies a write current supplied to the magnetic head 103 so as to record information on the magnetic disc 101. The head IC 108 also amplifies a read current which is generated by the magnetic head 103 due to changes in a magnetic flux density provided by the magnetic disc 101.
FIG. 2A is a plan view of an arm structure including the arm 104; FIG. 2B is a side view of the arm structure shown in FIG. 2A. The arm structure comprises a plurality of arms 104 so as to support a plurality of magnetic heads 103. Hereinafter, a description will be given of one of the arms 104. The connection line comprises a lead wire 107a and an FPC 107b. The magnetic head 103 is connected to an end of the FPC 107b via the lead wire 107a. The FPC 107b is provided with wire patterns, and the head IC 108 is connected to the wire patterns. Thus, the magnetic head 103 is connected to the head IC 108 via the lead wire 107a and the wire patterns of the FPC 107b.
FIG. 3A is a plan view of the FPC 107b; FIG. 3B is a plan view of an end of the FPC 107 which is located on the side of the magnetic head 103; FIG. 3C is a plan view of an end of the FPC 107b which is connected to a circuit board.
The FPC 107b comprises a flexible board 201 on which a printed wire pattern 200 is formed. The flexible board 201 has a connection end 203 and a connection end 207 which are opposite ends of the flexible board 201. The printed wire pattern 200 is formed on the flexible board 201 between the connection ends 203 and 207. The printed wire pattern 200 comprises a wire pattern 202 on the side of the connection end 203 and a wire pattern 206 on the side of the connection end 207. A head IC mounting portion 205 is formed between the wire pattern 202 and the wire pattern 206.
An end of the lead wire 107a is connected by solder to a terminal 204 formed on the connection end 203 of the FPC 107b. The opposite end of the lead wire 107a is connected to the magnetic head 103. The head IC 108 is soldered to the head IC mounting portion 205. Accordingly, a reproduction signal transmitted to the wire pattern 202 is supplied to the head IC 108. The head IC 108 amplifies the reproduction signal and outputs the amplified signal to the wire pattern 206. Accordingly, the amplified signal is transmitted to the connection end 207.
The connection end 207 of the FPC 107b is connected to a circuit board (not shown in the figure). A pull-up circuit 109 and a read channel circuit (RDC) 110 are formed on the circuit board. The pull-up circuit 109 pulls up the output of the head IC 108 and supplies the output to the RDC 110.
FIG. 4 is a circuit diagram of the pull-up circuit 109. The pull-up circuit 109 comprises pull-up resistors R1 and R2 and AC coupling capacitors C1 and C2. An end of each of the pull-up resistors R1 and R2 is connected to a power source line Vcc, and the other end of each of the pull-up resistors R1 and R2 is connected to the head IC 108 so as to pull up an output signal. An end of the AC coupling capacitor C1 is connected to the end of the pull-up resistor R1 which is connected to the head IC 108. The other end of the AC coupling capacitor C1 is connected to the RDC 110. An end of the AC coupling capacitor C2 is connected to the end of the pull-up resistor R2 which is connected to the head IC 108. The other end of the AC coupling capacitor C2 is connected to the RDC 110. Each of the AC coupling capacitors C1 and C2 eliminates a DC component of the output of the head IC which is pulled up by the respective pull-up resistors R1 and R2, and supplies the output to the RDC 110.
The RDC 110 demodulates the signal supplied from the head IC 108 via the pull-up circuit 109. The signal demodulated by the RDC 110 is supplied to a microprocessor unit (MPU) 111 (refer to FIG. 1). The MPU 111 is connected to the RDC 110, a digital signal processor (DSP) 112 and a hard disc drive connector (HDC) 113. The MPU 111 processes information recorded on or reproduced from the magnetic disc 101. The MPU 111 also controls a rotation of the magnetic disc 101 and positioning of the magnetic head 103 in accordance with the information read from the magnetic disc 101 by the magnetic head 103.
The DSP 112 generates digital data for controlling rotation of the spindle motor 102 in accordance with digital data supplied by the MPU 111 which determines rotational speed of the magnetic disc 101. Additionally, the DSP 112 generates digital data for controlling operation of the voice coil motor 106 in accordance with digital data supplied by the MPU 111 which determines a position of the magnetic head 103. The digital data for controlling the rotational speed of the spindle motor 102 and the digital data for controlling the operation of the voice coil motor 106 are supplied to a digital analog converter (DAC) 114. The DAC 114 converts the digital data for controlling the spindle motor 102 into an analog signal, and supplies the analog signal to a spindle motor (SPM) drive circuit 115. The SPM drive circuit 115 generates a drive signal for driving the spindle motor 102, and supplies it to the spindle motor 102. Thus, the spindle motor 102 is rotated by the drive signal so that the magnetic disc 101 rotates in the direction indicated by the arrow A. The DAC 114 also converts the digital data for controlling the voice coil motor 106 into an analog signal, and supplies the analog signal to a voice coil motor (VCM) drive circuit 116. The VCM drive circuit 116 generates a drive signal for driving the voice coil motor 106, and supplies it to the voice coil motor 106. Thus, the voice coil motor 106 is operated by the drive signal so that the arm 104 is moved in the directions indicated by the arrows B so as to locate the magnetic head 103 at a designated position.
The HDC 113 is connected between the MPU 111 and a connector 117 which is connected to an external device. The HDC 113 controls data transmission between the magnetic disc apparatus 100 and the external device such as a host computer 120.
In the above-mentioned conventional magnetic disc apparatus, the reproduction signal is supplied from the magnetic head 103 to the head IC 108 via the lead wire 107a and the FPC 107b. Thus, the connection line between the magnetic head 103 and the head IC 108 is relatively long. Each of the lead wire 107a and the FPC 107b has a capacitance which may decrease a cutoff frequency for the reproduction signal. That is, the capacitance of the lead wire 107a and the FPC 107b deteriorates the high-frequency characteristic of the signal transmission line. Additionally, the head IC 108 itself has a frequency characteristic which may deteriorate the high-frequency characteristic of the signal transmission line.
FIG. 5 is a graph representing a frequency characteristic of a signal supplied to the read channel circuit (RDC) of the conventional magnetic disc apparatus. The high-frequency characteristic in a high-frequency range is shifted in a direction indicated by an arrow C as shown in FIG. 5 due to the capacitance of the lead wire and FPC and the frequency characteristic of the head IC. That is, the high-frequency component of the reproduction signal is deteriorated due to the characteristic of the connection line between the magnetic head and the read channel circuit provided in the circuit board.